164 ME. F. J. COLE ON THE STRUCTURE AND MORPHOLOGY OF 



is seen lying internal to and above Meckel's cartilage *. In front the external man- 

 dibular passes still further downwards, finally taking up a position ventral to Meckel's 

 cartilage and slightly dorsal to the hyomandibular canal. It is still accompanied by 

 trigeminal fibres, which, however, pass to their destination anterior to the termination 

 of the external mandibular. Tlie twigs to sense organs 1 and 2 pass tiirough the same 

 foramen at the anterior extremity of the dentary. 



(•i) Lateralis Canal. 



The lateralis lateral line nerve j^ursues a course somew^hat analogous to that of the 

 buccal. It gives off a supra-temporal branch, which corresponds to the otic, and like it 

 supplies one of the termini of its canal, and then splits into a dorsal and a A'entral ramus 

 which may be said to coincide with the two divisions of the buccal trunk. The dorsal 

 ramus innervates the anterior or abdominal lialf of the lateralis canal with its associated 

 pit organs, and the ventral ramus does the same for the posterior or caudal moiety of the 

 canal. Both rami are of course typical lateral line nerves, and as such are composed of 

 special sensory and not of typical somatic sensory fibres. They may be united by one or 

 more commissures, and together form wdiat are referred to in the text-books as the 

 " cutaneous branches of the vagus." 



Lateralis Trunk. 



This large nerve emerges from the medulla at a high level immediately behind the 

 lateral line ganglion of the trigemiuo-facial complex, in front of the root of the 

 glossopharyngeus and some distance in front of and dorsal to the root of the A^agus. The 

 latter nerve arises by a double root from the medulla distinctly ventral and posterior to 

 the lateralis. On leaving the medulla the lateralis passes downwards and backwards, and 

 soon swells into the large lateralis ganglion. It still continues the same course and 

 passes external to the root of the glossopharyngeal, to which, as it passes, it gives a very 

 small twig which accompanies the pre-branchial division of the IXth. The lateralis 

 ultimately joins the vagus, Avhich it accompanies, lying external to it. Hitherto there 

 have been ganglion cells along almost the w hole of the length of the lateralis root, but 

 as soon as it reaches the vagus the ganglion cells largely disappear, and only a few are to 

 be seen. Coincident wdth the disajjpearance of cells in the lateralis root is their 

 appearance in the root of the vagus, in which they multiply as the nerve recedes from the 

 brain. Both nerves pass throiigh the same canal in the exoccipital, the vagus occupying 

 the anterior and internal position, and the lateralis stiU possessing a few ganglion cells. 

 No mixing of the two nerves was observed at any part. Outside the exoccij)ital foramen 

 the vagus root immediately enters the large compound (?) vagus ganglion, and there is 

 also a I'urther collection of ganglion cells on the lateralis in connection with, and at the 

 base of, its supra-temporal branch. 



* AUis (6, p. GIO) saj".s that this part of the ini'orior maxillary accompanies the " r. buccalis facialis," but this is 

 obviously a slip for " r. maudibularis eiternus facialis." 



